Injection Molding

An injection mold is a precision tool (usually steel or aluminum) with two halves that form a cavity. Molten plastic is injected in, cooled, and ejected as a finished part.
 • Core and cavity: the two mold halves that create the part shape when clamped shut.
 • Feed system: plastic typically flows through a sprue, runners, and a gate before entering the cavity.
 • Cooling + ejection: built-in cooling channels remove heat; ejector pins help push the part out.
 • Venting: small vents let trapped air escape to avoid burns and short shots.

Injection molding melts plastic pellets, injects the melt into a closed mold under pressure, cools it, then opens the mold to eject the part. The cycle repeats to make consistent parts at scale.
 • Clamp: the mold closes and stays shut under clamp force.
 • Plasticize: pellets melt and mix in a heated barrel and screw.
 • Fill + pack: molten plastic fills the cavity; pressure is held to reduce shrink marks.
 • Cool: the part solidifies against the mold surface.
 • Eject: the mold opens and the part is released; gates/runners may be trimmed if used.

It depends on part size, complexity, and expected production life. Tooling cost is driven by steel vs aluminum, number of cavities, slides/lifters, hot runners, tolerances, and surface finish. A quote needs a part file and volume target. One industry guide puts plastic injection molds anywhere from about $100 for low-volume 3D-printed tooling to $100,000+ for complex multi-cavity steel tools. Your part design and volume set the real number.
 • Part requirements: size, wall thickness, cosmetic surfaces, tolerances, and material choice.
 • Tool complexity: side actions (slides), lifters, unscrewing cores, inserts, and texture.
 • Production goals: expected annual volume, cycle time targets, and tool life expectations.
 • Runner strategy: cold runner vs hot runner (often higher upfront, different per-part economics).

To injection-mold ABS, keep the resin dry, use the material supplier’s processing window, and tune fill/pack/cool to avoid cosmetic defects and warpage. Gate design, venting, and uniform wall thickness matter as much as machine settings.
 • Moisture control: store and dry resin as required by the resin supplier to reduce splay and surface defects.
 • Design for flow: maintain consistent wall thickness; add ribs instead of thick sections to reduce sink.
 • Venting + gating: good venting prevents burns; gate location affects weld lines and appearance.
 • Cooling strategy: uneven cooling is a common cause of warp; mold temperature control is part quality control.

ABS can contain residual monomers and additives that may migrate in small amounts, depending on time, temperature, and what it contacts. For food-contact or regulated uses, choose a compliant grade and confirm with migration testing for your conditions.
 • Regulatory context: in the US, ABS for food contact is addressed in FDA food-contact regulations with specific limits/conditions.
 • Conditions matter: migration risk changes with temperature, contact time, and the type of food or solvent exposure.
 • Practical rule: don’t assume “ABS is safe” or “ABS is unsafe” in the abstract; specify the grade, use case, and compliance/testing standard.

Large plastic parts usually require higher clamp force, larger shot capacity, and careful design to control shrinkage and warpage. If the part is very large or hollow, thermoforming or rotational molding can be a better fit than injection molding.
 • Design controls: keep wall thickness consistent, use ribs/gussets wisely, and avoid thick mass that drives sink and long cooling.
 • Tooling + handling: large tools need robust cooling and ejection; part handling and fixturing become part of the process plan.
 • Process choice: very large panels often lean toward thermoforming; large hollow parts often lean toward rotational molding.